1. Field of the Invention
This invention relates to ultrasonic transduction and especially to a method and means for remote, contact-free, ultrasonic, non-destructive examination of test objects for flaws and acoustic discontinuities such as solid-to-gas or liquid-to-solid interface.
2. Description of the Prior Art
X-ray examination of test objects, such as jet and reusable rocket engines, for cracks or other flaws has disadvantages, such as expense, complexity, danger to human health, and inability to detect separations and disbonds perpendicular to the beam. Non-destructive examination can also be accomplished by inducing an ultrasonic wave in the test object by means of a piezoelectric transducer and analyzing the wave after its passage through the test object. However, the ultrasonic transducer must be held against the test specimen by the use of wetting or greasing compounds which means that the test object and transducer must be cleaned after the test. This adds labor, time and expense to the test procedure and sometimes leaves an undesirable residue. Also, the apparatus has to be disassembled if an interior component such as a blade or impeller is to be checked. Other types of examination for flaws require the test object to be cut and examined, so that the object is destroyed and cannot be used thereafter.